The present invention relates to devices for producing a as that can be used to perform a desired function such as inflating an air bag or inflatable in a vehicle and, in particular, to propellant compositions that are part thereof.
Systems that output one or more gases are known to utilize such gases for providing predetermined functions. For example, inflator systems are commonly used to inflate air bags in a vehicle. Inflators and accompanying air bag modules can be positioned at a number of different locations inside the vehicle, including adjacent the driver (driver side inflator), adjacent the front seat passenger (passenger side inflator), adjacent the sides of the driver and/or front seat passenger (side inflator) and above the side windows (curtain inflator). The design or configuration of each inflator depends on its location. For example, the driver side inflator is different in geometry from a passenger side inflator. Regardless of its location, a commercially acceptable inflator must have certain characteristics. Not only must an inflator properly supply inflation gases when activated to fill the air bag, the manufacture and assembly of the inflator should be as uncomplicated as feasible. Furthermore, the inflator must meet competitive cost requirements.
Notwithstanding the extensive number of inflators that have been advanced or devised for use in vehicles, the manufacturing/assembly and cost reduction benefits continue to be major objectives sought to be achieved in connection with the design and development of new inflators for use in vehicles. Consequently, it would be advantageous to provide inflators that meet such practical considerations, as well as provide other enhanced features. It would also be beneficial to apply such technology and features to applications other than vehicle inflators.
In accordance with the present invention, a gas generating apparatus is provided for generating at least one gas for a predetermined function. In one application, an inflator is provided that generates inflation gases for delivery to an inflatable or air bag. The inflator includes a propellant for generating the inflation gases when activated by an ignition assembly. In one embodiment, the propellant preferably is elongated, i.e., its length is substantially greater than its width. The ignition assembly is activated by a control signal indicative of the occurrence of a predetermined event related to vehicle impact or collision of at least a threshold force. When the propellant is elongated, it can be a number of elongated pieces of propellant or a single elongated piece. Regardless, each elongated propellant has a substantially greater length than its width and the ratio of length-to-width is greater than at east about 10, preferably about 100.
In one embodiment, the propellant has a porous composition that is sufficiently oxidized so that no unacceptable percentage of carbon monoxide and/or other toxic gases result after combustion of the propellant is completed. In this embodiment, the propellant includes a fibrous cellulose material or fibers to facilitate its extrusion and to promote the porosity of the propellant by minimizing shrinkage during drying. A cellulosic binder, such as hydroxypropylcellulose (HPC) dissolved in solvent such as alcohol, is used to suspend the solid ingredients and provide the appropriate rheology for extrusion. The HPC, together with the fibrous cellulose and a dispersal agent, constitute the binder system of the propellant, as well as fuels for the combustion reaction. The dispersing material or dispersal agent is also preferably used, in conjunction with the HPC, to prevent or substantially eliminate clumping of the fibrous cellulose component of the propellant composition when it is being formed. Hence, the HPC has at least two functions, namely, contributing to the binding of the propellant and assisting in the dispensing of the fibrous cellulose. The dispersing material can include a product identified as Cellulon(copyright), which is available from NutraSweet/Kelco Company, This is a fibrous cellulose material having a much smaller fiber size than the fibrous cellulose ingredient. The propellant may also include one or more other additives, such as known stabilizers and/or anti-oxidants.
In another embodiment of a propellant composition, no binder system is utilized to bind first and second materials together. Such a propellant composition comprises the first material that includes a fuel-rich component as at least the primary component thereof. The fuel-rich component is a secondary explosive. This propellant composition also includes the second material that comprises an oxidizer material as at least the primary component thereof. Preferably, the primary component is ammonium nitrate. The first and second materials are mixed together and contained in the inflator housing. When desired or necessary, a force is applied to the mixture within the inflator housing to withstand transportation vibrations and/or avoid rattle.
The inflator includes a confining member or pressure tube that surrounds the elongated propellant. In one embodiment, the confining member includes a number of layers. A number of holes are spaced at predetermined distances from each other along the length of the confining member. In that regard, such spaced holes are preferably created when seals or weakened areas of the confining member rupture or open when the propellant is ignited. In another embodiment, the holes are present before the propellant is combusted. The confining member length is equal, or substantially equal, to the length of the elongated propellant. The confining member is preferably made of a non-metallic material that can withstand a pressure of at least 3,000 psi and preferably 4,000 psi and greater. The confining member has an inner wall and the elongated propellant has an outer surface, with a gap or space disposed between this inner wall of the confining member and the outer surface of the elongated propellant. In one embodiment, the elongated propellant has a center bore located through the center longitudinal axis of the propellant. Both the gap and the center bore, when present, affect or contribute to the propagation of a combustion wave along the length of the elongated propellant. That is, when the propellant is ignited at one end thereof, a combustion wave is created that results in the combustion of the elongated propellant along a linear path defined by the length thereof. Among other factors, propagation of the combustion wave is a function of the size of the gap and the center bore, if any. More particularly, the propagation of the combustion wave should be at least 0.1 meter/msec. In conjunction with meeting this parameter, the ratio of the cross-sectional area of the propellant to the cross-sectional area of the inner diameter of the confining member must be within a particular range This ratio is in the range of about 0.10-0.60.
In one embodiment, the inflator further includes a timing member or tube that houses at least substantial portions of the confining member and propellant. The timing tube can be rigid or it can be flexible, e.g., made of a coated fabric of the like. The timing member controls flow of inflation gases to the air bag or inflatable. In that regard, the timing member includes one or more orifices through which inflation gases can pass when the propellant is ignited and products of combustion, including the inflation gases, are generated. The timing member regulates flow of the inflation gases to the inflatable at a desired rate. In the absence of the timing member, the inflation gases generated by the propellant contemplated by the present invention might result in an unacceptable rapid filling or pressurization of the inflatable with the inflation gases. If such an inflator were activated in a vehicle, the occupant experiencing such a rapid filling of the inflatable with inflation gases could be subject to a greater than desired pressure. Preferably, a number of orifices are formed along the length of the timing member. Because of the relatively rapid propagation of the combustion wave, inflation gases flow from the pressure tube into the timing tube very rapidly to fill the timing tube to a peak pressure. These gases stored in the timing tube can then readily pass through each of such orifices in the timing tube at substantially the same rate, with the time of passage of inflation gases through such orifices being relatively independent of the propagation rate in the pressure tube. The inflatable surrounds the timing member and therefore receives such inflation gases along its length at substantially the same rate to uniformly fill the inflatable along its length at substantially the same time. This uniform receipt of inflation gases results in the inflator itself filling the entire inflatable. Such filling is in contrast to certain portions of the inflatable being filled by other portions thereof using the inflation gases that have been received at one end of the inflatable and are caused to move to other parts of the inflatable by additionally received inflation gases. Like the confining member, the timing member is also preferably made of a non-metallic material that reduces its cost and package size.
In operation, the ignition assembly is activated which ignites the propellant near one end thereof. Propagation of the combustion wave along the length of the propellant occurs. Inflation gases are generated and pass through holes in the confining member. The confining member is sufficiently strong to resist any structural rupturing or breaking thereof, as well as there being little, if any, noticeable combustion of the confining member. Inflation gases that pass through the confining member holes enter the space or area between the outer surface of the confining member and the inner wall or surface of the timing member. Inflation gases reach the orifices in the timing member and are metered through them to fill the inflatable.
Based on the foregoing summary, a number of salient aspects of the present invention are readily discerned. The gas generating apparatus produces one or more gases and can be readily incorporated into any one of a number of systems that utilize the resulting gas. In one area of application, the gas generating apparatus is an inflator used in a vehicle that generates inflation gases. Such an inflator has fewer, less expensive parts, which are easily assembled and manufactured. The cost of the inflator is reduced in view of the relatively fewer parts. Propagation of a combustion wave associated with the generation of the inflation gases is controlled using the confining member that can withstand substantial pressures without rupturing. The confining member has a number of spaced holes that are present before and/or after activation of the propellant through which the inflation gases escape. Such holes increase in size after propellant ignition. The propagation rate has a sufficient magnitude to properly inflate the air bag or other inflatable. In addition to having fewer parts, the confining member and the timing member can be made of non-metallic materials thereby also reducing the cost of the inflator. Particularly when an elongated propellant is included, uniform filling of an elongated inflatable is achieved through the use of the spaced orifices in the timing member, which regulate the flow of inflation gases in connection with filling the inflatable. The propellant has a composition that is sufficiently oxidized to avoid the presence of toxic gases after combustion is completed. In one embodiment, the propellant composition includes a loose mixture of propellant grains and oxidizer materials. In another embodiment, the propellant composition includes fibrous cellulose or other porosity producing component(s), together with a dispersal agent. The fibrous cellulose is beneficial in providing a rigid but porous propellant composition that is readily extrudable, while the dispersal agent is advantageous in avoiding unwanted clumping and an improper mixture of the propellant composition. Such porosity is highly beneficial when the propellant includes ammonium nitrate.